Intro: How To: Make a Simple Crystal Radio
I know there is many on this topc but this is slightly different. Instead of using magnet wire, gelana, iron pyrite, germanium diodes, I have used a rusty knife blade (A craft knife with the snap of blades) and a pencil lead as a detector, a crystal Earphone as an earphone, Solid Cat 6 wire as the winding wire for the coil, hookup wire as an aerial and earth. Hope this shows you that you really can use anything to make this work. Im sorry for the lack of pictures in constuction (Im doing this in retrospective to start with)
Step 1: Matarials
This may end up as a running list as I improve/modify the radio.
For the Coil:
4 meters solid core Cat. 6 wire (4 twisted pairs)
3" OD PVC pipe
For the Cat's Whisker Detector:
1 old rust craft blade
1 HB (expierement) pencil
Small Piece of wood (to mount on)
3 wood screws (preferably cap but if you want to use counter sunk then you need custom metal washers too.)
LOTS of hook-up wire (I bought 25 meters and turned out that was only just enough)
Variable Capacitor (Mine was 60pf - 160pf)
Crystal Earphone (normal MP3 headphones won't work apparently but feel free to try them out)
Germanium Diode (for testing although not necessary)
Tools I used:
Number 8 wire (I think in america it might be called fencing wire otherwise google it)
My Sisters electronic board (I needed a Germanium Diode and a tuning capacitor. I no longer need the Germanium Diode and im buying a variable capacitor)
Solder (I guess you could call it a tool. Maybe if you considder it as an adhesive)
Automatic Wire Stripper (This is AMAZING!! If you dont have one then you need it. I strips wires and can cut them to. Saves me hours!!)
Step 2: Winding the Coil
This was VERY tedious. I recommend listening to the radio while doing this. After buying 4 meters of the Cat 6 wire I have to 'open it up' there were 4 twisted pairs and a plastic seperator thingy. After spending TOO much time unwinding the first pair, I convinced my sister to help. Im not sure how but she did another 2 in half the time it took me to do one. I wasn't watching her do it so I cant suggest how to do it faster. Onto the coil itself.
Step1: Drill 2 small holes (about 7mm apart) near one end (make sure the are following a winding pattern).
Step 2: Thread a small piece of the solid core wire into th two holes (push it through the Outside then back through to the outside from the center (sorry if this confuses you.)
Step 3: Start to wind the wire round up until you have 10 turns. Then you make a tap in the coil (make a loop then twist it together). Do this on the 16th, 24th, 32nd, 40th, 52nd, and 65th turns. Next continue to wind the coil untill you get to 80. Now drill two more holes as close as posible to the end of the coil and thread the end through. Thank God you have finished. You can also tape to hold the coil as you go.
Step 4: On the taps you have made you need to get the insulation off the twist them tightly. When you have 8 taps all nice and coppery you can tin the with solder.
Step 3: Cats Whisker Detector
The was called the cats whisker detector because in the original 'Crystal' radios the has a tiny metal (not always copper) touching a semi conducting mineral. This small wire was similar to a cats whisker. Im sure there is other kinds of detectors out there but I couldnt find them.
Step 1: Take the HB pencil (2B, 2H, or whatever else shoud work) and using a knife cut away the wood so you can get a piece of lead (mine would be about 1 1/4" long). Now using a knife, sharpn the pencil lead to a small point (im sure the smaller the better)
Step 2: Take a piece of copper wire (about 6 - 10" long) and strip all of the insulation off. Use this to bind the pencil lead to the paper clip (unbend it obviously). Now solder over the wire and you should get a nice strong joint (but dont test it to much. If you break the lead you may need to start over!
Step 3: Screw a small wood screw into the board (leave a little sticking up)
Step 4: Heat up the screw with a soldering iron and make a small pool of solder into it. Tin a small piece of hook-up wire and melt it onto the screw. Do the same thing with the paper clip (the non pencil end)
Step 5: Bend the paper clip out of the way and some how screw the rusty knife blade to the wood. On one of the screws you need to solder another wire onto it.
Step 6: Bend the paper clip to look similar to the one in either of the pictures (there needs to be a little bit of force onto the blade.
Step 4: Aerial and Earth
For the aerial you need it to be as high as possible and as long as possible. I had mine loop around the roof of the garage and then leading to my room. DO NOT let the end of the wire touch ANYTHING that may ground it. On mine I folded over and end and covered it with electrical tape (ask if you want a picture). For the earth a coper cold water pipe may be used. DO NOT use a gas pipe. Also, all houses SHOUD have an AC earth (in NZ anyway) and you could also use that. If all else fails just get a long (minimum of a meter/yard) piece of metal pipe/wire and force it into the ground.
Step 5: Wireing It Together and Tuning
At the end of this step we will end up with a working radio.
Step 1: Take the variable capacitor and snip on little tab off (if you have three) DO NOT CUT THE CENTER TAB!! If you do that then I WILL NOT work. Snip either the right or the left. you want the capacitance to go up as you turn it to the left.
Step 2: At the start of the coil attach the aerial with aligator clips (you may solder this on later when you know it works.)
Step 3: Attach one of the capacitor leads to the start of the coil and aerial.
Step 4: Attach the other side of the capacitor to the earth and the selector (selector comming soon. You may just use an aligator clip as the selector for now).
Step 5: Attach one lead from the earphone to the earth and the other to the wire connected to the knife blade on the detector.
Step 6: Attach the other lead from the Whisker Detector to the end of the coil.
Step 7: Attach the germanium diode in parallel with the detector and turn the capacitor until you can hear (even if faintly) a station. Un wire the germanium diode.
Step 8: Now move the pencil around till you can hear the station again (you ahve found a 'hot spot' and try to tune it so it is more audable.
Step 9: Continue to fiddle around with your radio and most of all HAVE FUN!!